BigPipe Demo broken against D8.1 HEAD

#2469431-230: BigPipe for auth users: first send+render the cheap parts of the page, then the expensive parts added a RouteMatchInterface argument to the BigPipeStrategy constructor. This was not added to the BigPipeDemoStrategy constructor at that time, so enabling this module against D8.1 HEAD causes WSODs

[Sat Mar 05 17:23:01.480569 2016] [:error] [pid 10078] [client 127.0.0.1:51229] Recoverable fatal error: Argument 3 passed to Drupal\\big_pipe\\Render\\Placeholder\\BigPipeStrategy::__construct() must implement interface Drupal\\Core\\Routing\\RouteMatchInterface, none given, called in big_pipe_demo/src/Render/Placeholder/BigPipeDemoStrategy.php on line 44 and defined in core/modules/big_pipe/src/Render/Placeholder/BigPipeStrategy.php on line 103